Microwave-Assisted Preparation of White Fluorescent Graphene Quantum Dots as a Novel Phosphor for Enhanced White-Light-Emitting Diodes

Graphene quantum dots (GQDs) with white fluorescence are synthesized by a microwave-assisted hydrothermal method using graphite as the precursor. A solution-processed white-light-emitting diode (WLED) is fabricated using the as-prepared white fluorescent GQDs (white-light-emitting graphene quantum dots, WGQDs) doped 4,4-bis(carbazol-9-yl)biphenyl as the emissive layer. White-light emission is obtained from the WLED with 10 wt% doping concentration of WGQDs, which shows a luminance of 200 cd m(-2) at the applied voltage of 11-14 V. Importantly, an external quantum efficiency of 0.2% is achieved, which is the highest among all the reported WLED based on GQDs or carbon dots. The results demonstrate that WGQDs as a novel phosphor may open up a new avenue to develop the environmentally friendly WLEDs for practical application in solid-state lighting.